As we mentioned in the second part, about the J2M1, "since there are no known photos of the other prototypes it is unknown if they were in any way different." Actually there is one more photo that could be of one more J2M1 prototype. It is featured on p.23 top of FAOW #61, p.57 lower of Gakken #29 and p.36 upper of Model Art #832 (aka Profile #11). According to all sources it shows one of the J2M1 prototypes but with a canopy exactly like the one fitted to mass-produced J2M2 "Raiden".
The tail marking is "ヨC-106" (YoC-106) and this indicates that it is one of the test aircraft that were sent to the Yokosuka based 301Ku, one of the very first "Raiden" units. The photo was taken at the end of 1943 or the begining of 1944. According to MA#832, although J2M1 prototypes were painted hairyokushoku this one is painted "kiiro" (yellow) in compliance of the official IJNAF painting instructions of October 6, 1942 that ordered all trainer and test aircraft to be painted in this colour. You will notice that there is one very important difference between ヨC-106 and the other J2M1 prototype, the コ-J2-6; the fuselage hinomaru has a white surround. This is an indication that it was painted yellow (or orange-yellow), not hairyokushoku.
Gakken #29 states that if the number "6" of the tail marking is part of the serial number of the aircraft, then ヨC-106 could be the same sixth prototype, the コ-J2-6, but fitted with a different canopy. It is possible but no other source makes this suggestion. As we mentioned before official documentation is lacking.
Another difference with the コ-J2-6 is what appears to be wing cannon(s?). FAOW explains that this was a Type 99 20mm 2Go Model 1.
Below is artwork created again by our friend Devlin Chouinard.